Element: [Bug Report] Clearable el-select shows clear button on hovering when value is null

[topclaudy]

Element UI version

2.4.0

OS/Browsers version

Chrome 66, Firefox 60.0.1

Vue version

2.5.16

Reproduction Link

https://jsfiddle.net/p04y83r4/

Steps to reproduce

Go to the reproduction link
Hover the clearable select

What is Expected?

No clear button

What is actually happening?

It shows the clear button even when the value is null

[wangjun521]

Remove your clearable attribute

[topclaudy]

I want it to be clearable (when it's not null or not empty)

[wangjun521]

还想让他是个下拉选择框还得是可清除的 有没有感觉你这种需求很奇葩啊亲
And you want him to be a drop-down box and you have to be able to clear it and you have to feel like you have a weird need